Rock cutting and excavation machines have been developed for various specific applications including mining, trenching, tunneling, foundation drilling, road milling, etc. Typically, a drive body in the form of a rotatable drum or drill head comprises a plurality of replaceable cutting bits that provide the points of contact for the material or mineral face.
For example, a mobile mining machine includes a rotatable cutting head with the cutting bits provided on rotating drums. As the bits contact the surface of the seam they occasionally break and inevitably wear resulting in decreased cutting inefficiency and a need for replacement. It is therefore desirable to mount the cutting bits at the cutting head (or drive body) via releasable mounting assemblies that enable the bits to be replaced conveniently and quickly during servicing and repair.
Cutting bit (alternatively termed ‘cutting pick’ or ‘tool pick’) mountings are described in U.S. Pat. No. 3,342,531; U.S. Pat. No. 3,627,381; U.S. Pat. No. 4,343,516; WO 2010/027315; US 2011/0278908 and EP 2514918.
Cutting bits have been developed that may be considered to fall in at least two general categories. A first general type comprises a nose portion attached at one end of an elongate shaft whilst a second type comprises a bit head having an inner cavity that fits onto an end of an ‘adaptor’ that forms an elongate shank. In both cases, the shaft or shank is received within and held at the mount body by a form retainer.
However, conventional methods of mounting the cutting pick (of the types mentioned) to the mount or drive body involve press-fit, threaded nut or locking washer arrangements typically provided at a rearward end of the cutting bit shaft or adaptor. These conventional means for retaining the shaft or adaptor at the mount body suffer from a number of disadvantages. In particular, press-fit sleeves are typically cumbersome to install and remove and typically require additional specialised tools for quick removal. A threaded nut or general screw thread arrangement is disadvantageous within a dusty environment where the threads become blocked quickly due to the dirty environment in which the cutter is operating. Additionally, due to the machine and cutting vibrations during operation, nut and screw thread fastenings require constant retightening to ensure the cutting bits do not become dislodged. Conventional locking washer arrangements are similarly disadvantageous in that during use, the washers wear resulting in the undesirable movement of the shaft or adaptor at the holder body which also acts to reduce cutting efficiency and damage to the pick holder. Accordingly, what is required is a cutting bit retaining assembly that addresses these problems.